The present invention relates to a magnetic recording tape cartridge. More particularly, it relates to a magnetic recording tape cartridge wherein at least one slip sheet is placed between the inside surface of the cartridge case and the tape pack.
Hitherto, in a magnetic recording tape cartridge there is known to provide a slip sheet between the inside surface of the cartridge case and a tape pack surface so as to prevent loss of levelling of an edge of a roll of magnetic tape wound around a hub. For example, as shown in FIG. 1, U.S. Pat. No. 3,712,559 discloses a constitution of a slip sheet 1 having a plurality of radially extending ribs 2 placed between the inside bottom surface of a case 3 which constitutes the cartridge and the surface 4 of the tape pack 5. In the said patent, each rib 2 of the slip sheet is extended from the hole 6 to accommodate the annular wall 7 which supports a hub 8 to the peripheral edge 9 of the slip sheet 1 and freed at the respective ends 2a and 2b. Accordingly, each rib 2 is apt to be flattened under the weight of the tape pack 5 as indicated in an alternate long and short dash line in FIG. 2, making it difficult to keep the edge level of the tape pack 5 at a fixed position.
Moreover, in the conventional slip sheets considerations on the positions for forming the convex ribs 2 and their numbers have been deficient because of the insufficient recognition of the relation between the factors to cause fluctuations of the hub 8 and the convex rib 2. For example, despite the fact that the tension of the magnetic recording tape 10 applied to the tape pack 5 is an important factor to cause fluctuations of the hub 8, no sufficient recognition has been made on the relationship between the position at which the tension acts and the position of the convex rib 2. For these reasons, in the conventional slip sheet 1, the convex ribs 2, though provided, have not been successful in displaying the desired effect.
An object of the present invention is to provide a magnetic recording tape cartridge of a construction wherein at least one slip sheet is placed between the inside bottom surface of the cartridge case and the hub around which a magnetic tape is wound, designed to suppress effectively the fluctuation of the hub in the course of the use and to take up the magnetic recording tape uniformly at all times.
Another object of the invention is to provide a magnetic recording tape cartridge provided with a slip sheet in which the ribs are so formed that each convex rib is closed with its both ends, thereby preventing a deformation of the ribs.
A further object of the invention is to provide a magnetic recording tape cartridge in which the ribs formed on the slip sheet are arranged to the optimum positions so as to permit winding of the magnetic recording tape uniformly.